A turning wheel, a straight push

Follow the motion from the part that turns to the part that moves along a line, and mark the place where one becomes the other. Which quantities would you need to measure to analyse it?

Follow the turning to the line in al-Jazari's double-piston pump. Hill's translation of Category V, Chapter 5 describes two drive alternatives: a vertically mounted vaned wheel turned by flowing water like a mill, or a horizontal paddle wheel driving a gear train. Both end in a disc with an eccentric dowel ². The slotted lever is housed in a triangular mulberry-wood box, pivoting at a corner and receiving the rotating dowel in its slot ³. The chapter explains successive portions of the rotation: changing dowel position produces lever oscillation and movement of its connected rods, not a piston that rotates like the wheel ³. The text offers two ways to drive one mechanism, and no requirement to install both ².

No passage in the records gives al-Jazari's reason for these two machines. They show the practical problem of the scoop lifter: raising water from a well or pool, a task associated with supplying water to a channel ^4 5. In it, gears carry rotation to a pin that moves through a slot in the ladle stem, raising and lowering the scoop ⁴. If operated as described, the scoop would move water upward without a person carrying each scoop by hand, but the sources do not document who operated a historical installation or who received its water ⁴.

When was the book finished? The encyclopedia dates completion to 1205, and al-Hassani gives 1206, while the Science Museum catalogue calls the published design c. 1205 ^6 7 8. Hill's introduction gives 1204 or 1206 based on differences among manuscripts ⁹. The record keeps the differences and repairs none. They are dates of the book, not of a pump built in a particular well ^9 10.

The scoop lifter survives as a picture. The Met holds folio 55.121.11, and its record dates the copy to 715 AH/1315 CE and identifies Farrukh ibn Abd al-Latif as copyist ¹¹. The image shows a manuscript drawing, not the physical machine described in the text ¹¹. The folio does not provide a complete engineering plan, verified scale, or proof that the design was constructed as drawn ^11 4.

Sadettin Ökten emphasizes double action, the conversion of rotation into reciprocation and what he calls the first known use of a suction pipe, and he calls the pump an early example for later pumps and the steam engine ⁶. Should a physics teacher repeat such a claim, and how would you answer the objection that students remember an origin story better than a caveat?

• The double-piston pump: the drive, the slotted lever and the paired cylinders.
• The animal-powered scoop lifter: a pin that slides in the slot of the ladle stem.
• Al-Jazari: his book, its six divisions and the dates it is given.